Who We Are

Minnehaha Creek Watershed District is a local unit of government
responsible for managing and protecting the water resources in
one of the largest and most heavily-used urban watersheds in Minnesota.

The watershed stretches 178-square miles from St. Bonifacius
to south Minneapolis and includes Lake Minnetonka, the
Minneapolis Chain of Lakes, Minnehaha Creek, and Minnehaha
Falls. It includes eight major creeks, 129 lakes, and thousands of
wetlands. Learn more about the watershed.

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Stormwater Management Rule

1. POLICY

(a) Promote abstraction of precipitation
and stormwater runoff where feasible for the purposes of improving water
quality, increasing groundwater recharge, reducing flooding, and promoting the
health of native and designed plant communities and landscapes;

(b) Preserve, maintain and improve the
aesthetic, physical, chemical and biological composition of surface waters and
groundwater within the District;

(c) Limit or reduce stormwater
runoff from drainage within the watershed to decrease the negative effects of land-disturbing
activities on surface water quality and flooding;

(e) Promote the preservation and
use of native vegetation for the purpose of stormwater runoff abstraction and
pollutant load reduction;

(f) Promote nondegradation of water
quality from new development and improvement in water quality from redevelopment;
and

(g) Promote the management of
stormwater on site for the purposes of providing local groundwater recharge and
maintaining natural hydrology.

2. REGULATION

No one may create new or replace existing impervious surface or change
the contours of a parcel of land in a way that affects the direction, peak rate,
volume, or water quality of runoff flows from the parcel or subdivide a parcel of
one acre or more in size into three or more lots without first submitting a
stormwater management plan to the District and securing a permit from the
District approving the plan. New development
is subject to sections 3 and 7-11 below (see Table 2). Redevelopment is subject
to sections 3-5 and 7-11 below (see Tables 3 and 4). Subdivision of land is
subject to section 3-5 and 7-11, as applicable. Linear Transportation Projects are
subject to sections 3 and 6-11 below (see Table 5).

Activity
subject to this rule on adjacent sites under common or related ownership shall
be considered in the aggregate, and the requirements applicable to the activity
under this rule will be determined with respect to all development that has
occurred on a site, or on adjacent sites under common or related ownership,
since the date this rule took effect (January 2005).

The
following activities are exempt from this rule:

(a) SINGLE FAMILY HOMES: Construction or reconstruction of
a single- family home.

(b) NEW DEVELOPMENT: New development
for a residential, commercial, industrial or institutional use (see Table 2):

(1) that will result in less than
20 percent impervious surface over the site; or

(1) on a site that is less than five acres
in size that will result in at least a ten percent reduction in impervious
surface; or

(2) on a site of five acres or greater
where the proposed activity disturbs less than 40 percent of the site and results
in at least a ten percent reduction in impervious surface.

(d) LINEAR TRANSPORTATION PROJECTS:
Construction of a new or reconstruction of an existing road, trail, sidewalk, utility,
or other linear transportation project (see Table 5):

(1) that will create less than
10,000 square feet of new impervious surface; or

(2) for the construction of
sidewalks and trails that will not exceed 12 feet in width and will
be bordered on the downgradient side(s) by a pervious buffer averaging at least
one-half the width of the sidewalk or trail.

3. STORMWATER MANAGEMENT PLAN GENERAL
REQUIREMENTS.

A stormwater management
plan submitted to the District must meet the following requirements, subject to
the provisions in sections 4-8:

(1) NEW DEVELOPMENT/LINEAR
TRANSPORTATION PROJECTS: Activity
subject to this rule for new development or linear transportation projects shall
result in no net increase in phosphorus loading from existing conditions, except
that:

i.
For a parcel in existing use for row crop agriculture
or feedlot, new development shall result in no net increase in phosphorus
loading from the site as modeled in meadow condition.

(2) REDEVELOPMENT: Phosphorus
control must be provided in accordance with subsection 3(c)(2), where applicable.

(b)
RATE CONTROL.

(1) Activity subject to this rule
shall result in no net increase in the peak runoff rate for the 1-, 10- and 100-year
design storms where stormwater discharges across the downgradient site
boundary, compared to the rate for the site in its existing condition, except
that:

i.
For a parcel in use for row crop agriculture or feedlot,
new development shall result in no net increase in the peak runoff rate from
the site as modeled in meadow condition.

(2) Peak runoff rates for the 1-, 10-
and 100-year design storms may not increase within a specific drainage area of
the site so as to create or exacerbate drainage or erosion problems.

(c) VOLUME CONTROL.

(1) The stormwater management plan
must provide for the abstraction of the first one inch of rainfall from the
site's impervious surface. Credit toward compliance with the one inch volume
control standard will be calculated by the applicant using industry accepted
hydrologic models and Appendix A: Volume Abstraction Credit Schedule, following
guidance provided in the Minnesota Pollution Control Agency's Minnesota Stormwater Manual.

(2) Where an applicant demonstrates
that it is infeasible to meet the one inch abstraction requirement through use
of volume control credits pursuant to subsection 3(c)(1), the stormwater
management plan must provide for abstraction of runoff to the greatest extent
feasible, and at least 0.5 inches, and phosphorus control in an amount equivalent to that which would be
achieved through abstraction of one inch of rainfall from the site's impervious
surfaces. To demonstrate infeasibility of providing abstraction pursuant
to 3(c)(1), the applicant must submit a completed Abstraction Analysis containing
at a minimum the following information:

i. A
narrative that lists and explains the variables that limit the feasibility of
providing one inch of volume control for runoff from the site's impervious
surface. These variables may include but
are not limited to unified soil classification, soil contamination, proximity
to bedrock, proximity to groundwater, proximity to existing utilities, spatial
constraints, zoning requirements, and financial considerations.

ii. A narrative and conceptual
plan(s) that describes and discusses how reasonable modifications to the size,
scope, configuration or density of the project would influence the feasibility
of providing one inch of volume control for runoff from the sites impervious
surface.

iii. An explanation of efforts undertaken
by the applicant to accommodate or remove the constraints that influence the
feasibility of providing one inch of volume control for runoff from the site's
impervious surface.

(3) The volume of runoff draining to a
landlocked receiving area may not increase due to a project unless the
applicant can demonstrate that any additional runoff volume from the project
will be effectively abstracted. In addition, the applicant shall either own or
have proper rights over the landlocked property receiving runoff from the
project area. Back-to-back 100-year runoff events will be used to analyze
holding capacity and high-water elevation for landlocked areas.

(1) BMPs addressing the potential water resource impacts
associated with the proposed activity must be incorporated to limit creation of
impervious surface, maintain or enhance on-site infiltration and peak flow
control and limit pollutant generation on and discharge from the site. BMPs may
include site design, structural and non-structural practices.

(2) BMPs must be designed and installed in accordance with
generally accepted design practices and guidance contained in the Minnesota
Pollution Control Agency's Minnesota
Stormwater Manual and its subsequent revisions.

(e)
HIGH WATER ELEVATION.

(1) All applications shall provide at least two vertical
feet of separation between low openings of structures and the 100-year high
water elevations of stormwater BMPs and waterbodies.

A stormwater management plan
submitted to the District that proposes through redevelopment to decrease or result
in no net increase in impervious surface must meet the following requirements (see
Table 3):

(a) For sites that are one acre or
less, Best Management Practices are required in accordance with subsection 3(d);

(b) For sites that are between one
acre and five acres and the proposed activity disturbs less than 40 percent of
the site, Best Management Practices are required in accordance with subsection
3(d);

(c) For sites that are between one
acre and five acres and the proposed activity disturbs 40 percent or more of
the site, the stormwater management plan must meet the volume control requirement
in subsection 3(c) and the phosphorus control requirement in subsection
3(a)(2), where applicable;

(d) For sites that are greater than
five acres and the proposed activity disturbs less than 40 percent of the site,
Best Management Practices are required in accordance with subsection 3(d);

(e) For sites that are greater than
five acres and the proposed activity disturbs 40 percent or more of the site, the
stormwater management plan must meet the volume control requirement in subsection
3(c) and the phosphorus control requirement in subsection 3(a)(2), where
applicable.

5. REDEVELOPMENT REQUIREMENTS - INCREASED IMPERVIOUS SURFACE.

A stormwater management plan submitted to the
District that proposes to increase impervious surface through redevelopment
must meet the following requirements (see Table 4):

(a) For sites that are one acre or
less, Best Management Practices are required in accordance with subsection 3(d);

(b) For sites that are greater than
one acre and the proposed activity disturbs less than 40 percent of the site and
results in an increase in impervious surface of less than 50 percent, the
phosphorus control requirements of subsection 3 (a), rate control requirements
of subsection 3(b) and volume control requirements of subsection 3(c) apply to
the area of increased impervious surface;

(c) For sites that are greater than
one acre and the proposed activity disturbs 40 percent or more of the site, or results
in an increase in impervious surface of 50 percent or more, the phosphorus
control requirements of subsection 3(a), rate control requirements of subsection
3(b), and volume control requirements of subsection 3(c) apply to the entire
site.

6. LINEAR
TRANSPORTATION PROJECT REQUIREMENTS (see Table 5).

(a) The construction of a new road,
trail, sidewalk, utility, or other linear transportation project that will
create 10,000 square feet or more of impervious surface must meet the
phosphorus control requirements in accordance with subsection 3(a), rate
control requirements in accordance with subsection 3(b) and volume control
requirements in accordance with subsection 3(c);

(b) Linear Reconstruction Projects
that will increase the impervious area within the project limits by between
10,000 square feet and one acre from existing conditions must meet the phosphorus control requirements
in accordance with subsection 3(a) and rate control requirements in accordance
with subsection 3(b) for the area of increased impervious surface;

(c) Linear Reconstruction Projects
that will increase the impervious area within the project limits by one acre or
more from existing conditions must meet the phosphorus control requirements in
accordance with subsection 3(a), rate control requirements in accordance with subsection
3(b), and volume control requirements in accordance with subsection 3(c) for
the area of increased impervious surface.

7. REGIONAL STORMWATER MANAGEMENT.

(a) An applicant may comply with
this rule by providing equal or greater phosphorus control, rate control, or
volume control through a regional or subwatershed plan approved by the
District; such a plan must provide for an annual accounting to the District of
treatment capacity created and utilized by projects or land-disturbing
activities within the drainage and treatment area of the plan.

(b) District approval of a regional
or subwatershed plan will be based on a determination that:

(1) the use of a regional facility
in place of onsite stormwater management will not result in adverse impacts to local
groundwater or natural resources located upstream of the regional facility,
including, but not limited to, reduced water quality, altered wetland
hydrology, changes to stream velocities or baseflow, erosion, or reduced
groundwater recharge; and

(2) the plan incorporates onsite
BMPs as necessary to mitigate impacts and provide local benefits not provided
by the regional facility.

(c) Individual project sites
utilizing a regional facility to meet phosphorus, rate, or volume control requirements
must incorporate BMPs on the project site in accordance with subsection 3(d).

(d) The applicant, before
commencing any land-altering activity, must demonstrate that it holds the legal
rights necessary to discharge to the stormwater facility or facilities in the
plan, and that the facility or facilities are subject to a maintenance document
satisfying the requirements of section 11.

8. IMPACT ON
DOWNSTREAM WATERBODIES.

(a) No new point source may discharge
to a waterbody without pretreatment for sediment and nutrient removal.
Pretreatment may be provided by non-structural means. An activity changing flow
that discharges from an existing point source is not a new point source.

(b) No activity subject to this rule may
alter a site in a manner that results in a(n):

(1) Increase in the bounce in
water level for any downstream lake or wetland beyond the limits specified in
Table 1 below based on management classification, during a rainfall event of
critical duration with a return frequency of 1, 10, or 100 years.

(2) Increase in the duration of
inundation for any downstream lake or wetland beyond the limits specified in
Table 1 below based on management classification, during a precipitation event
of critical duration with a return frequency of 1, 10, or 100 years.

(3) Change in the elevation of the
runout control of any lake or wetland beyond the limits specified in Table 1
below based on management classification.

Table 1: Impacts
on downstream waterbodies

Wetland Management
Class/

Waterbody

Permitted Bounce
for 1-, 10-, and 100-Year Event

Inundation Period
for 1-Year Event

Inundation Period
for 10- and 100-Year Event

Runout Control

Elevation

Preserve

Existing

Existing

Existing

No change

Manage 1

Existing plus 0.5 feet

Existing plus 1 day

Existing plus 2 days

No change

Manage 2

Existing plus 1.0 feet

Existing plus 2 days

Existing plus 14 days

0 to 1.0 ft above existing runout

Manage 3

No limit

Existing plus 7 days

Existing plus 21 days

0 to 4.0 ft above existing runout

Lakes

Existing

N/A

N/A

No change

9. FINANCIAL ASSURANCE.

(a) A performance
bond, letter of credit or other financial assurance, consistent with the
District Financial Assurance Rule, may be required for any project that
requires the installation of stormwater best management practices. The
financial assurance shall be maintained until the stormwater best management
practice has been constructed and stabilized in accordance with District rules
and as shown on a set of as built drawings submitted to the District.

10. REQUIRED
EXHIBITS.

(a) Plans certified by a professional
engineer registered in the State of Minnesota and reflecting the following
items shall accompany the permit application (one set of plans must be full
size; one set must be reduced to a maximum size of 11"x 17"; provide electronic ArcGIS or CADD files
when available):

(1) Property lines and delineation
of lands under ownership of the applicant.

(2) Delineation of the
subwatershed contributing runoff from off-site and proposed and existing
subwatersheds on-site.

(8) Stormwater runoff volume and
rate analyses for the 1-, 10- and 100- year design storms for existing and
proposed conditions.

(9) All hydrologic, water quality,
and hydraulic computations completed to design the proposed stormwater
management facilities including runoff volume abstractions.

(10) Delineation of any flowage
easements or other property interests dedicated to stormwater management
purposes, including, but not limited to, county or judicial ditches.

(b) For applications proposing
infiltration, a soil sampling plan and the resulting identification,
description, permeability, and approximate delineation of site soils. Investigation methods shall include soil pits
or hand augers. Borings at the location of the infiltration facility must
extend at least five feet deeper than the proposed bottom elevation of the
infiltration facility.

(c) For applications proposing tree
preservation or planting, a site map showing existing trees larger than six
inches in diameter, including species, diameter, and associated drip lines
(canopy area). Tree map must designate trees to be removed and trees to be
added.

(i) A declaration and maintenance
agreement in conformance with section 11.

11. MAINTENANCE.

(a) All stormwater management
structures and facilities must be designed for maintenance access and properly
maintained in perpetuity to assure that they continue to function as designed. Permit applicants must
provide a maintenance plan that identifies and protects the design, capacity
and functionality of onsite and offsite stormwater management facilities;
specifies the methods, schedule and responsible parties for maintenance;
provides for the maintenance in perpetuity of the facility; and contains at a
minimum the requirements in the District's standard maintenance declaration.
The plan will be recorded on the deed in a form acceptable to the District. A
public entity assuming the maintenance obligation may do so by filing with the
District a document signed by an official with authority.

Table 2: Stormwater management requirements for new
development

Site Size

Impervious Surface

Requirements

< 1 acre

N/A

None

≥ 1 acre

< 20% of site

None

≥ 20% of site

Phosphorus Control, Rate Control, and
Volume Control

Table 3: Stormwater management requirements for redevelopment
resulting in a decrease or no change in impervious surface

(2) Volume infiltrated during a rainfall event shall
not be credited towards the abstraction volume requirement. This is a simple approach
for designers and for reviewers to verify conformance to the standard; a stormwater
model is not needed for calculations. This is a conservative assumption because
infiltration of stormwater in Minnesota
is an evolving practice. MCWD will continue to research current trends, collect
and analyze monitoring data, and utilize modeling and engineering methods to
assess the effectiveness of the standards to achieve the water quality goals of
the District.

(3) Percent rainfall
interception shall be determined using results from the City of Minneapolis, Minnesota Municipal
Tree Resource Analysis. Percentages
for the species studied are listed below.
If desired tree species is not listed, the applicant shall use the
median value provided below or provide documentation by a certified arborist to
support a different percent interception.

Average Percent Rainfall Interception by
Tree Species

Species

Average Percent Rainfall
Interception

Green Ash

13

Sugar Maple

8

Norway Maple

8

Littleleaf Linden

12

American Elm

18

Honeylocust

6

American Basswood

10

Northern Hackberry

6

Ginkgo

4

Silver Maple

16

Elm

21

White Ash

10

Basswood

14

Red Maple

7

Median

10

(4) Tree canopy area must be documented
as part of the permit application submittal.

(5) Granting ½ credit for new
trees is intended to encourage preservation of trees over tree removal and replacement.

(8) For SCS TR-55 cover type "herbaceous mixture," additional rainfall of approximately 0.5 inches generates
no runoff if the hydrologic condition is improved from "fair" to "good." Credit will not be granted for "tree
preservation" and "enhancement of pervious area." The applicant must designate the desired
abstraction practice.

(9) The Minnesota Stormwater Manual reports that nutrient removal (total
phosphorus) is approximately half as effective for filtration as
infiltration.